A common rail for accumulating highly pressured fuel for engines are constructed as shown in FIGS. 4 and 5.
In a common rail J1 shown in FIG. 4, a common rail housing is provided with a pressure accumulation chamber J2 in which highly pressured fuel is accumulated, and a plurality of fuel delivery ports J3 extending tangentially from the accumulation chamber J2. The longitudinal center axis D of the delivery ports J3 is positioned perpendicular to the longitudinal center axis B of the cylindrical body J4. The longitudinal center axis A of the pressure accumulation chamber J2 is offset by a given distance R against and in parallel with that B of the cylindrical body J4.
By offsetting the longitudinal center axis A of the pressure accumulation chamber J2 against that B of the cylindrical body J4, the internal opening of the delivery ports J3 is made oval and the circumferential length of the same is extended, so that the stress concentrated at the internal opening of the delivery ports J3 is reduced. This serves to improve the durability of the cylindrical body J4 against the accumulated pressure.
In a common rail J1 shown in FIG. 5, a common rail housing is made by forging and joint fitter J7 of a pipe joint body J5 (provided with a variable resistance valve J6) is formed in the same body with a cylindrical body J4. The longitudinal center axes A, B of a pressure accumulation chamber J2 and the cylindrical body J4 are positioned coaxially, and the longitudinal center axis D of a delivery port J3 is positioned a given distance R away from the longitudinal center axis B of the cylindrical body J4.
By offsetting the longitudinal center axes D of the delivery ports J3 against that B of the cylindrical body J4, the internal opening of the delivery ports J3 is made oval and the circumferential length whereof is extended, so that the stress concentrated at the internal opening of the delivery ports J3 is reduced.
Also by shaping a cross section of a pressure accumulation chamber oval, the internal opening of the delivery ports is made oval and the circumferential length whereof is extended, so that the stress concentrated at the internal opening of the delivery ports J3 is reduced. This common rail is disclosed in U.S. Pat. No. 6,497,219B2 (JP2001-295723).
These serves to improve the durability of the cylindrical body J4 against the accumulated pressure.
In the common rail J1 shown in FIG. 4, the pressure accumulation chamber J2 is positioned against the center axis B of the cylindrical body J4, so that the pressure accumulation chamber J2 cannot be formed by rotating the cylindrical body J4. Thus the processing method of the cylindrical body J4 is limited and the productivity of that is low.
The thickness of the cylindrical body J4 is not uniform. This may cause some distortion in the cylindrical body J4 by the heat caused by welding of the joint fitter J7 or the heat processing.
In the common rail J1 shown in FIG. 5, the position of the joint fitter J7 as well as that of the delivery port J3 is also offset against the longitudinal center axis of the cylindrical body J4. Thus, in manufacturing the cylindrical body J4, the die parting plane G is set on the longitudinal center axis D (line F) of the delivery port J3 which is offset a distance R away from the longitudinal center axis B of the cylindrical body J4. Thus, the die for forging the cylindrical body J4 is asymmetric and complex shape which causes the difficulty in making and shortens the life of the die.
The cylindrical body J4 endures tensile strength generated along the circumference thereof by the high-pressure fuel accumulated in the chamber J2. Accordingly, the tensile stress concentrates around the delivery port J3. That is, the durability of the cylindrical body J4 around the delivery port J3 is low.